Probably the cultural divide, or rather the gulf between Chinese culture and Islam, though there are probably a number of factors involved. But you are progressively walking the conversation away from your original point which you have failed to defend so I wish you well as you ponder such questions.
Cultural divide didn’t stop Islam from spreading to disparate cultures like those of South East Asia, Africa or Eastern Europe, so that cannot be the reason for the curtailment.
The original point still stands that Islam has no single mortal enemy. Plain reason is good enough to defeat it.
I wish you well, too, and hope you continue to ponder upon these questions just as surely as I will.